Guarding the lone arrested terrorist, Ajmal Kasab, and also ensuring that the man is consistent in his confessions is probably one of the biggest challenges for both the Mumbai Anti Terrorist Squad and the Intelligence Bureau.

Both the IB and the ATS, which are interrogating Kasab simultaneously, say Kasab is a tough nut to crack and gives out information in bits and pieces. The bigger worry for both these agencies is to ensure that the man is consistent in his statements and also ensure that he does not keep changing his stance every now and then.

According to the IB, the ATS questions Kasab first and there is only a two-minute gap before the IB moves in to resume the questioning. ATS and IB sources told rediff.com that the short gap between interrogation by the two agencies is deliberate so that Kasab does not have the time to think up new versions. There have been times when he has told the ATS one thing and when the IB steps in he has given an entirely new spin to the Mumbai terror strikes.

This, according to the ATS, is due to the training he received as a fidayeen to dodge interrogation by constantly changing his version and misguide the investigating agencies.

Which is why both the agencies are hardly giving Kasab any time by himself to think up what to say next. "We ensure that our questions are specific and to the point. We expect him to answer only those questions that we ask and a questionnaire has been prepared in this regard. We go through the same questions over and over again, and the biggest challenge for us is to ensure that Kasab is consistent in his replies," both agencies say.

Apart from getting details about the terror network and its modus operandi, his nationality is also a prime aspect of the interrogation. "Kasab has consistently maintained that he is from Pakistan and we have ample proof of it. We want to subject him to a narco-analysis test so that we can seal this issue," the ATS says.

In custody Kasab is said to be very unsteady. There are times when he is extremely enthusiastic and at times he has shown signs of depression and goes completely quiet, ATS sources say. "We are not taking any chances and are keeping a 24x7 vigil on him. A constable is with him all the time."

Kasab is being moved to undisclosed locations from time to time due to security reasons. "He is definitely on the hit list and hence we do not want to take any chances," ATS sources said.